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Magnetization relaxation, ac susceptibility, dc magnetization and magnetoelectrical transport measurements have been carried out on Al3+-doped manganites La 0.5 Ca 0.5 Mn 1- x Al x O 3- δ (x = 0.05, 0.07, 0.09, 0.10, 0.15). Experimental results suggest that nonmagnetic Al3+ substituting Mn suppresses the ferromagnetic phase and induces a charge ordered antiferromagnetic phase. The coexistence and competition of these two kinds of interactions result in a spin-glass like state in x = 0.1 and 0.15 system. Obvious hysteresis was observed in both magnetization and resistivity versus temperature and magnetic field curves, suggesting an inhomogeneous metastable phase transition. Upon applying a magnetic field of H C A-F, the Al3+-doped samples undergo an irreversible metamagnetic transition from the charge ordering antiferromagnetic insulating to ferromagnetic metallic phase in the low temperature region. Phase diagram in the H C - T plane has been determined according to the magnetization and magnetoelectric transport measurements. The magnetic disorders and antiferromagnetic matrix produced by Al3+ dopants and spontaneous oxygen vacancies play an important role in the pinning of the FM phase. [ABSTRACT FROM AUTHOR]

The Al3+ doping effects on the ferromagnetic metallic state of La 0.55 Ca 0.45 MnO 3 have been studied by preparing the La 0.55 Ca 0.45 Mn 1- x Al x O 3- δ (x = 0, 0.05, 0.1, 0.15) ceramics. Various measurements such as ac susceptibility, relaxation, magnetization and resistivity were performed to study the magnetic and magnetotransport properties. The magnetic disorder produced by the Al3+ dopants and the oxygen vacancies suppress the long range ferromagnetic ordering and induce a short range charge ordered antiferromagnetic clusters, leading to a phase separated behavior in the Al3+-doped samples. A Griffith-like behavior is observed due to the occurrence of short range ferromagnetic clusters in the paramagnetic phase. The 15% Al3+ doping sample exhibits a spin-glass state. The 10% Al3+ doping system is blocked in a metastable state upon cooling at zero field, and a sharp metamagnetic transition is induced by applying a high magnetic field, in which the antiferromagnetic phase is transformed into ferromagnetic phase and the ferromagnetic clusters grow in size. The ferromagnetic domains grows rapidly when applying a high magnetic field. Once the conducting ferromagnetic domains are interconnected throughout the sample, a percolative insulating-to-metallic state transition would occur, accompanied by a sharp drop in resistivity. • Al3+ doping induces charge ordered AFM clusters in La 0.55 Ca 0.45 Mn 1- x Al x O 3- δ. • The magnetic disorder caused by Al3+ doping suppresses the long rang FM ordering. • The AFM clusters transform into FM phase via field driven metamagnetic transition. • Percolative insulator-metallic transition occurs when applying a magnetic field up to H C. [ABSTRACT FROM AUTHOR]

[Display omitted] • The charge ordering (CO) phase in La 0.5- x Bi x Ca 0.5 MnO 3 is enhanced with Bi3+ doping. • The enhancement of CO phase is explained by the s-p hybridization model. • Pulsed high magnetic fields up to 50 T were used to study the CO phase melting. • H C - T phase diagrams of La 0.5- x Bi x Ca 0.5 MnO 3 (0 ≤ x ≤ 0.2) were obtained. La 0.5- x Bi x Ca 0.5 MnO 3 (x = 0, 0.05, 0.1 and 0.2) compounds have been prepared to study the effects of Bi3+ substitution on the structure, magnetic and magnetotransport properties. Experimental results show that Bi3+ dopants have induced a distinct lattice distortion and phase separated state in which the long range ferromagnetic order turns into short range ferromagnetic clusters, and the charge ordering/antiferromagnetism and ferromagnetic clusters coexist in the system. Bi3+ doping induced disorders lead to the presence of a Griffith-like phase. The hybridization between Bi3+-6s orbitals and O2–-2p orbitals produces a localization of O2–-2p electrons and lattice distortion, which plays an important role in favoring charge ordering state and multiple magnetic ordering. The charge ordering antiferromagnetic collapses into ferromagnetic phase through a metamagnetic transition with applying a sufficiently high magnetic field. A T - H C phase diagram was determined based on the magnetization and electrical transport measurements, in which the phase boundary is figured out. [ABSTRACT FROM AUTHOR]